1. Field of the Invention
The present invention relates to secondary batteries, and, more particularly, to electrode assembly short circuit prevention.
2. Description of the Related Art
In general, a secondary battery, which, unlike a primary battery which is unable to be recharged, is rechargeable and dischargeable, and is widely employed in high-end electronic apparatuses such as mobile communication terminals, laptop computers, camcorders, and the like.
Particularly, since a lithium secondary battery has a high operating voltage and high energy density per unit weight, the market share of the lithium-ion battery in the battery market is increasing.
The lithium secondary battery typically includes positive electrode active materials such as lithium oxide and negative electrode active materials such as carbon. The lithium secondary battery may have various shapes. For example, there are cylinder type lithium secondary batteries, prismatic type lithium secondary batteries, and pouch type lithium secondary batteries.
Each of the cylinder and prismatic type lithium secondary battery cell may include an electrode assembly accommodated in a can and a cap assembly sealing a top opening of the can. The pouch type lithium secondary battery may include an electrode assembly and an aluminum pouch accommodating the electrode assembly.
The electrode assembly is wound by interposing a separator between a positive electrode plate and a negative electrode plate. Each of the positive electrode plate and the negative electrode plate includes an electrode collector and a coated portion which is formed by coating active materials on surfaces of the electrode collector. Also, each of the positive and negative electrode plates includes a non-coating portion which is absent the active materials on the electrode collector. Electrode tabs are welded and fixed to the non-coating portions.
The separator is disposed between the positive electrode plate and the negative electrode plate to insulate therebetween. The separator may be made of polyethylene, polypropylene, or a composite film of polyethylene and polypropylene.
Heat is generated inside the secondary battery when there is overcharge generated during the charge of the secondary battery or when there is a short circuit between the electrodes. Since the negative electrode tab typically made of dissimilar metal with the negative electrode collector is welded to each other at the non-coating portion of the negative electrode plate, internal resistance (IR) is increased and heat is concentrated.
When heat is concentrated around the negative electrode tab, the separator positioned at the region where the negative electrode tab is positioned may be melted or contracted. The separator would typically be excessively contracted at the corners of the separator so that a short circuit may occur between corners of the negative and positive electrode plates.
Specifically, in the case of a short circuit between the positive electrode collector and the negative electrode coating portion, a fire and/or an explosion could occur in the secondary battery and safety of the secondary battery would be significantly deteriorated. Since energy density of the secondary battery is increasing as a capacity of the secondary battery increases, the likelihood of a short circuit between the electrode plates caused by heat at the electrode tabs due to an internal short circuit becomes greater.